$-6df - 9e - 9f - 6 = e - 4f + 2$ Solve for $d$.
Explanation: Combine constant terms on the right. $-6df - 9e - 9f - {6} = e - 4f + {2}$ $-6df - 9e - 9f = e - 4f + {8}$ Combine $f$ terms on the right. $-6df - 9e - {9f} = e - {4f} + 8$ $-6df - 9e = e + {5f} + 8$ Combine $e$ terms on the right. $-6df - {9e} = {e} + 5f + 8$ $-6df = {10e} + 5f + 8$ Isolate $d$ $-{6}d{f} = 10e + 5f + 8$ $d = \dfrac{ 10e + 5f + 8 }{ -{6f} }$ Swap the signs so the denominator isn't negative. $d = \dfrac{ -{10}e - {5}f - {8} }{ {6f} }$